1. Field of the Invention
The present invention relates to rotating media storage devices (RMSDs). More particularly, the present invention relates to an RMSD that utilizes reduced bit number wedge identification techniques.
2. Description of the Prior Art and Related Information
Computer systems rely on rotating media storage devices (RMSDs), which often employ a moveable head actuator to frequently access large amounts of data stored on the media. One example of an RMSD is a hard disk drive. A conventional hard disk drive has a head disk assembly (“HDA”) including at least one magnetic disk (“disk”), a spindle motor for rapidly rotating the disk, and a head stack assembly (“HSA”) that includes a head gimbal assembly (HGA) with a moveable transducer head for reading and writing data. The HSA forms part of a servo control system that positions the transducer head over a particular track on the disk to read or write information from that track.
Each surface of each disk conventionally contains a plurality of concentric data tracks angularly divided into a plurality of data sectors. In addition, special servo information is provided on each disk or on another disk to determine the position of the moveable transducer head. The most popular form of servo is called “embedded servo” wherein the servo information is written in a plurality of servo wedges that are angularly spaced from one another and interspersed between data sectors around each track of each disk. Each servo wedge generally comprises a track identification (ID) field, a wedge ID field having a unique binary encoded wedge ID number to uniquely identify the wedge, and a group of servo bursts (an alternating pattern of magnetic transitions) which the servo control system samples to align the moveable transducer head with or relative to a particular servo track or one or more corresponding data tracks.
The servo control system moves the transducer head toward a desired track during a coarse “seek” mode using the track ID field as a control input. Once the transducer head is generally over the desired track, the servo control system uses the servo bursts to keep the transducer head over that track in a fine “track follow” mode. The transducer head generally reads the servo bursts to produce a position error signal (PES).
Further, during track following mode, the moveable transducer head repeatedly reads the wedge ID field of each successive servo wedge to obtain the unique binary encoded wedge ID number that uniquely identifies each wedge of the track. In this way, the servo control system continuously knows where the moveable head is relative to the disk. Unfortunately, the unique binary encoded wedge ID number includes a relatively large number of bits to uniquely identify each wedge of the track. Today, in order to uniquely identify a wedge, the number of required bits are N; where N can be determined as: wedges <=2^N.
As an example, to uniquely identify up to eight wedges on a track, N must equal at least 3. In other words, each unique binary encoded wedge ID number requires at least three bits. Thus, a typical coding scheme would be (wedge #/unique binary encoded wedge ID number): 0/000; 1/001; 2/010; 3/011; 4/100; 5/101; 6/110; 7/111. Or as another example, for the case of identifying thirteen wedges on a track, N must equal at least 4. Thus, a typical coding scheme would be (wedge #/unique binary encoded wedge ID number): 0/0000; 1/0001; 2/0010; 3/0011; 4/0100; 5/0101; 6/0110; 7/0111; 8/1000; 9/1001; 10/1010; 11/1011; 12/1100. Of course for tracks with even more wedges, the unique binary encoded wedge ID numbers are even larger. For example, for the case where there are 256 wedges, N must equal at least 8. However, at the same time, in the very competitive disk drive market, disk drive manufacturers are continuously striving to reduce overhead data stored in the servo wedges in order to free up more disk space for storing data in the data sectors around each track of the disk.